52% students in Scotland aged 25 found to iodine deficient (Combet, 2014)

You need to incorporate seafish, seafood or seaweed into your diet. You only need the equivalent of half a teaspoon of seaweed a day (or just 1 x 500mg capsule of a good quality organic seaweed). Dairy has a little, eggs around 87 mcg (tiny) and both chlorine and fluorine - everyday chemicals - displace the little iodine that you'll be getting if you don't eat seafood. Potassium iodide in salt is not the same as chelated iodine from seaweed and in countries where it is part of a national supplementation program they find it tends to increase the incidence of over-active thyroid. Your minimum RI is 150 mcg and the safe WHO upper limit is 1100 mcg. The iodine patch test is not a reliable indicator, only a blood test but far better just to monitor what you are eating. There's a useful article on iodine use and safety by Napiers the Herbalists who did some proper research on iodine in seaweed, link is here http://www.napiers.net/safe-iodine-levels-in-seaweeds.html

The needed iodine should be ideally being
consumed from diet. I think supplementing iodine is not a good option at all.
It can be very dangerous in case of autoimmune thyroid response. There are
potentially many risks involved in supplementing Iodine. Some symptoms or signs
of iodine deficiency include cold intolerance, fatigue, hypothyroidism, weight
gain etc.

If you're not eating much iodine in your food, and it's not in your salt, you could probably use some more iodine in your life.

I like slicing up salty kombu squares with scissors and throwing it in with a stir fry. Or, you can make a tea out of it (konbu-cha) and use that like soy sauce. Or, mix in some bonito flakes or dried anchovies / sardines and you've got some awesome dashi stock. I've also got some kelp granules that mix well into a seasoning mix. I suppose cranberries would do, too.

The only 'DIY test' that I've seen was about putting a patch of iodine on the skin and waiting to see how long until it 'absorbs'. The issue was that it had more to do with evaporation rather than absorbtion (IIRC) so it was not a useful measure of determining how much iodine your body 'absorbed'...and that's still assuming the original premise was correct.